Cellular radio communications systems are increasingly employed to provide wireless voice and data communications to a number of mobile units or subscribers. Cellular radio communications systems include both analog cellular systems, such as the "AMPS" system, and, more recently, digital cellular systems, such as the pan-European "GSM" system. These systems, and others, are described in a book entitled Dual Mode Cellular by Harte, published by P. T. Steiner Publishing Co., Bridgeville, Pa. (1992).
A cellular radio communications system generally includes one or more cellular telephones, one or more radio base stations and a Mobile Telephone Switching Center (MSC). A typical cellular radio communications system can include hundreds of radio base stations, thousands of cellular telephones and one or more MSC's. A cellular radio communications system includes a number of spaced apart radio zones referred to as cells. Each cell includes a radio base station for transmitting and receiving messages to and from cellular telephones which are located within the cell range.
Each cell of the cellular radio communications system typically includes a plurality of duplex voice channels over which cellular telephone messages are carried. Each cell is also provided with a number of control channels to control the operation of the cellular telephones and the assigned voice channels. Accordingly, through the cellular radio communications system, a duplex radio communication signal or link can be established between two cellular telephones or, between the cellular telephone and the wire line telephone.
As used herein, the term "cellular telephone" encompasses a wide variety of portable telephone devices which access a cellular radio communications system. Cellular telephones include mobile telephones that are hand held or of a bag phone variety and permanently mounted car cellular telephones. The term "cellular telephone" also include terminals which provide functions in addition to those of a cellular telephone, such as facsimile, data communications, data processing, word processing applications and other personal communication systems functions. These highly functional cellular telephones are often referred to as "Personal Communication Systems."
Each radio base station generally includes a control unit and an associated antenna. With respect to the cellular telephones located within the cell range, the base station functions chiefly to relay messages to and from the cellular telephones. The radio base station also supervises the quality of the communications link with the cellular telephones. A typical radio base station is Model No. RBS882 manufactured by Ericsson Radio Systems AB, Stockholm, Sweden for the CMS8800 cellular mobile telephone system. A full description of this analog cellular network is provided in Publication No. EN/LZT 101 908 R2B, published by Ericsson Radio Systems AB.
A number of base stations are connected to a single MSC which acts as the central coordinating element of the cellular system. The MSC includes a cellular processor and a cellular switch connected to the Public Switched Telephone Network (PSTN) to allow communications between the cellular telephones and wire line telephones. The MSC can also be associated with a Home Location Register (HLR). The HLR includes storage means for storing data relating to the subscribers of the cellular system. This data can include the telephone number of the subscriber as well as any specific services requested by the subscriber, such as call waiting or call hold. The HLR can also include processing means for manipulating the stored subscriber data.
A feature node can also be associated with the MSC of a cellular radio communications system or with another associated communications network, such as the PSTN. For example, the feature node can be incorporated within or associated with the HLR. Even if the feature node is associated with another communications network, such as the PSTN, the cellular radio communications network can access the feature node via the interconnection between the MSC of the cellular radio communications system and the PSTN or other communications network.
A feature node provides predetermined functions to the cellular telephones or the telephones associated with the PSTN, such as, for example, establishing an efficient communications link between telephones, such as via intermediate radio base stations, or providing voice-controlled speech information and number translation services as well as facilitating the establishment of conference telephone calls. Still further, a feature node can provide paging services for the user of a cellular telephone and can facilitate the establishment of alternative communications links if the primary communications link is unavailable. A feature node is described, for example, in more detail in U.S. patent application Ser. No. 018,268 entitled "A Method Of Establishing Cooperation With A Functionality" and U.S. patent application Ser. No. 018,223 entitled "A Method Of Organizing Communication", both of which were filed on Feb. 16, 1993 and both of which are incorporated herein by reference.
Due in part to the mobility of cellular telephones, numerous users of a cellular radio communications system carry a cellular telephone with them while they are conducting other activities. For example, many users have hand held cellular telephones which they carry with them throughout the day. Other users have mobile telephones that can be of either a bag phone variety or a permanently mounted car cellular telephone which permit the subscriber to communicate while in a vehicle. Accordingly, the cellular telephone user can be reached while they are performing a great variety of activities simply by placing a telephone call to the user's cellular telephone.
In response to the alert of the cellular telephone, the user, if they are in the vicinity of the cellular telephone, can answer the telephone call and begin voice communications with the calling party. Alternatively, if the user does not desire to presently respond to the alert and begin voice communications with the calling party, the user can simply ignore or not respond to the alert. Still further, the user can redirect the incoming telephone call by transferring the telephone call to another party or to a answering device to which the cellular telephone has previously been assigned.
In some instances, the user of the cellular telephone desires to converse with the calling party, but is unable to interrupt their present activities and begin communications with the calling party. For example, the user may be involved in a meeting which is near completion or the user may be involved in a driving activity which demands their full attention, such as passing a large truck on a narrow road. In these instances, the user can establish voice communications with the calling party and inform them that they will be with them in a moment. The user can then place the telephone call on hold, thus closing the speaker and the microphone of the cellular telephone, and complete their present activities. Once completed, the user can resume communications with the calling party.
However, the user can sometimes be involved in particularly demanding activities and is unable to conveniently or safely respond, even momentarily, to the incoming telephone call. In these instances, the user may desire to converse with the calling party, but must ignore the alert of the cellular telephone to complete their present activities. Thus, the user must either return the telephone call at a later time if the calling party left a message or must wait for the calling party to again attempt to contact the user. In either case, communications between the cellular telephone and the source telephone are, at best, significantly delayed.